Pedestrian-vehicle impact events are unfortunate but known occurrences. It is estimated that for vehicle-to-pedestrian collisions, eighty percent of serious injuries occurred to the pedestrian's head while thirty-seven percent of moderate injuries were suffered by lower extremities. (BMJ. May 22 2002: 324 [7346]: 11 45-1148)
The front edge of the vehicle hood is typically a relatively stiff area that impacts an adult's upper leg during a pedestrian-vehicle impact event. In a pedestrian-vehicle impact event involving a small child, the child's head may also collide with the front edge of the vehicle's hood.
The vehicle front and specifically the front overhang are designed to identify vehicle class and model type. In the case of the modern sports car, the front end is typically designed such that the vehicle has an overall low profile and a large hood to accommodate a high-power engine and associated powertrain. The front overhang of regular sedans and sports utility vehicles are designed to be stiff enough so that the damage to the front end during a low speed crash is not substantial. Larger vehicles, such as trucks, are often designed to enhance the sizes of the vehicle's grille and engine compartment, thus exaggerating the appearance of power and toughness. Such design characteristics can increase challenges associated with pedestrian impact protection.
The kinematics of a pedestrian during an impact depend on the characteristics of the vehicle front, its speed and the size of the pedestrian. If the center of gravity of a standing or walking pedestrian is higher than the leading edge of the vehicle, then the pedestrian's body may at least partially wrap around the vehicle front or may be lifted into the air as a result of vehicle contact. In general, the center of gravity of the pedestrian is most commonly higher than the leading edge of the vehicle, while the lifting of a pedestrian most commonly occurs during a high speed impact.
In the circumstance where an adult pedestrian at least partially wraps around the vehicle front it is the pedestrian's upper leg that is often impacted by the edge of the hood causing injury to the upper leg. If the impact event involves a child then the child's head or other body parts could impact the forward edge of the hood causing serious injury.
Known tests, such as the EuroNCAP pedestrian protection test protocol, include measures to protect the upper leg from impacting the hood (or bonnet) leading edge (“BLE”). The challenge in this test is that the impact velocity, angle as well as impact kinetic energy and legform mass are determined by look-up diagrams in the test protocol. Employed standards are based on the bonnet leading edge height (“BLEH”) and the bumper lead (“BL”) of the target vehicle at the impact location. The styling of a vehicle is determined at an early stage of a vehicle program which can result in a high initial kinetic energy (“KE”) level in the upper legform test.
To absorb legform KE by the front of the vehicle, there should be sufficient energy absorbing (“EA”) space. However, the stiffness requirements of the front structure and the components packaged at the front may not give sufficient EA space. This brings greater challenges to meeting upper legform requirements. Moreover a slight change in the final design in a local impact location can change the BLEH and the BL at that location and thus may lead to additional and costly late stage countermeasures to meet upper legform test requirements.
A known countermeasure to meet known pedestrian protection requirements is to incorporate a deployable hood into the vehicle. However, while providing arguable improvements in the current state of the art, some deployable hood designs could benefit from further enhancement of pedestrian protection at the front of the vehicle.
Accordingly, there is a need for a practical and effective system to protect pedestrians in a pedestrian-vehicle impact event. As in so many areas of vehicle technology there is always room for improvement related to the protection of pedestrians in a pedestrian-vehicle impact event.